My brother and I got an iZune thing where you can hook your iPod to your car's radio. why...?

Question

When I play it, but more so with a couple of songs in particular, I can hear my engine kind of whining louder than it usually does. It is definitely something with the engine, I think, as I can tell the difference between when I rev up or coast. What's going on? Draining the battery too much or something?

Answer 1

You can hear this in every radio. The interference is a matter of degree, the signal to noise ratio. It is simply interference from a variety of sources. The main source in an engine is the ignition. The on/off of the ignition generates square waves. The rapidly rising voltage produces a radio wave front which is picked up by the electronics in the MP3 player. Every radio has to accept noise to a certain degree, some more than others. You CAN do something about this, noise suppressors attached to various parts of the ingnition to suppress the wave fronts to an acceptable level for your device.  The very first radio transmitters were literally called "spark gap" transmitters, relying on the spark to intentionally generate the wave front, which was sensed in the receiver. Sparking in your engine does exactly the same thing, resulting in the interference.